Rapid curing epoxy compositions

ABSTRACT

The present invention provides a curable composition comprising (1) at least one epoxy compound containing at least one vicinal-epoxy group and (2) at least one catalyst selected from lithium or Group II metal salts of a non-nucleophilic acid. The present invention further provides an active epoxy curing catalyst composition.

BACKGROUND OF THE INVENTION

Epoxy compositions and their curing techniques are well-known and thepatents issued on curabble epoxy compositions number in the hundreds.Known curing agents include, among many others, polycarboxylic acids andanhydrides, amines, polyamides, imidazoles, and the like. Representativecuring agents are described in U.S. Pat. No. 3,336,241. These curingagents may be employed with one or more catalysts or accelerators suchas the stannous salts of monocarboxylic acids.

It will be appreciated that each and every one of the known epoxy-curingsystems exhibits advantages over other systems, and, as importantly,disadvantages over the same systems. There is, of course, a continuingneed to develop better epoxy curing compositions.

An epoxy curing system has how been found which is not only simple andproduces rapid curing, but the resulting cured epoxy compositionsexhibit excellent physical properties.

Accordingly, the present invention provides a curable epoxy compositioncomprising (1) an epoxy resin and (2) a curing amount of at least one"hard cation" catalyst.

SUMMARY OF THE INVENTION

The present invention provides a curable composition comprising (1) atleast one epoxy compound containing at least one vicinal-epoxy group and(2) at least catalyst selected from the group consisting of lithium andGroup II metal salts of a non-nucleophilic acid. The present inventionfurther provides an active epoxy curing catalyst composition.

DESCRIPTION OF THE PREFERRED EMBODIMENT

Suitable polyepoxides useful in the present compositions comprise thosecompounds containing at least one vicinal epoxy or oxirane group, i.e.,at least one ##STR1## group. These polyepoxides may be saturated orunsaturated, aliphatic, cycloaliphatic, aromatic or heterocyclic and maybe substituted if desired with non-interfering substituents such ashalogen atoms, hydroxyl groups, ether radicals, and the like. They mayalso be monomeric or polymeric.

For clarity, many of the polyepoxides and particularly those of thepolymeric type are described in terms of epoxy equivalent values. Themeaning of this expression is described in U.S. Pat. No. 2,633,458. Thepolyepoxides used in the present process are preferably those having anepoxy equivalency greater than 1.0.

Various examples of liquid polyepoxides that may be used in the processof the invention are given in U.S. Pat. No. 2,633,458 and it is to beunderstood that so much of the disclosure of that patent relative toexamples of polyepoxides is incorporated by reference into thisspecification.

Other suitable polyepoxides are disclosed in U.S. Pat. Nos. 3,373,221and 3,377,406 and so much of the disclosure relevant to examples ofepoxy compounds is incorporated by reference into this specification.

Preferred polyepoxides are the glycidyl polyethers of polyhydric phenolsand polyhydric alcohols, especially the glycidyl polyethers of2,2-bis(4-hydroxyphenyl)propane having an average molecular weightbetween about 300 and 3,000 and an epoxide equivalent weight betweenabout 140 and 2,000.

Other suitable epoxy compounds include those compounds derived frompolyhydric phenols and having at least one vicinal epoxy group whereinthe carbon-to-carbon bonds within the six-membered ring are saturated.Such epoxy resins may be obtained by at least two well-known techniques,i.e., by the hydrogenation of glycidyl polyethers of polyhydric phenolsor (2) by the reaction of hydrogenated polyhydric phenols withepichlorohydrin in the presence of a suitable catalyst such as Lewisacids, i.e., boron trihalides and complexes thereof, and subsequentdehydrochlorination in an alkaline medium. The method of preparationforms no part of the present invention and the resulting saturated epoxyresins derived by either method are suitable in the presentcompositions.

Briefly, the first method comprises the hydrogenation of glycidylpolyethers of polyhydric phenols with hydrogen in the presence of acatalyst consisting of rhodium and/or ruthenium supported on an inertcarrier at a temperature below about 50° C. This method is thoroughlydisclosed and described in U.S. Pat. No. 3,336,241, issued Aug. 15,1967.

The hydrogenated epoxy compounds prepared by the process disclosed inU.S. Pat. No. 3,336,241 are suitable for use in the presentcompositions. Accordingly, the relevant disclosure of U.S. Pat. No.3,336,241 is incorporated herein by reference.

The second method comprises the condensation of a hydrogenatedpolyphenol with an epihalohydrin, such as epichlorohydrin, in thepresence of a suitable catalyst such as BF₃, followed bydehydrohalogenation in the presence of caustic. When the phenol isBisphenol A, the resulting saturated epoxy compound is sometimesreferred to as "diepoxidized hydrogenated Bisphenol A," or more properlyas the diglycidyl ether of 2,2-bis(4-cyclohexanol)propane.

In any event, the term "saturated epoxy resin", as used herein shall bedeemed to mean the glycidyl ethers of polyhydric phenols wherein thearomatic ring structure of the phenols have been or are saturated.

An idealized structural formula representing the preferred saturatedepoxy compounds is as follows: ##STR2## wherein n has a value so thatthe average molecular weight of the saturated polyepoxide is from about350 to about 3000.

Preferred saturated epoxy resins are the hydrogenated resins prepared bythe process described in U.S. Pat. No. 3,336,241. More preferred are thehydrogenated glycidyl ethers of 2,2-bis(4-hydroxyphenyl)propane,sometimes called the diglycidyl ethers of2,2-bis(4-cyclohexanol)propane.

Other examples include the glycidyl novolac resins, i.e., thephenol-aldehyde condensates, as described in U.S. Pat. No. 2,658,885.

CATALYSTS

The hard cation non-nucleophilic anion catalysts useful in the presentcomposition include lithium and Group II metal salts of anon-nucleophilic acid. A "non-nucleophilic" acid is defined herein tomeans that (1) a 10% by weight water solution has a pH of <1.0 and (2)the anion portion of the acid does not easily participate indisplacement reaction with organic halides.

The preferred Group II metal (alkaline earth metal) salts are calciumand magnesium.

Suitable non-nucleophilic acids include fluoboric, fluoarsenic,fluoantimonic and fluophosphoric acids.

Accordingly, suitable hard cation non-nucleophilic anion salts include,LiBF₄, Ca(BF₄)₂, Mg(BF₄)₂, LiPF₆, Ca(PF₆)₂, Mg(PF₆)₂, LiSbF₆, LiAsF₆ andthe like.

Very preferred hard cation non-nucleophilic anion catalysts are LiBF₄and Ca(BF₄)₂.

The amount of catalyst (curing agent) utilized will be a curing orhardening agent. In general, from about 0.05 to about 15 parts per onehundred parts by weight (phr) of polyepoxides is employed with fromabout 0.1 to about 10.0 phr being preferred, and from about 0.5 phr toabout 2.0 phr being especially preferred.

The present compositions may be prepared by various techniques. If, forexample, the instant compositions are to be utilized within a shorttime, they can be simply prepared by mixing all the components, thenadding one or more of the customary additives such as solvents; fillers;reinforcement fibers; mats and bars; pigments; flame retardant agents;antioxidants; plasticizers; extenders; thixotropic agents, etc., andthen molding and curing the resulting composition. Even more effectivecuring (hardening) can be achieved when the metal salt is applied to afinely divided inorganic carrier. Simply, the metal salt is suspended ina solvent to which one or more inorganic materials have been added.After blending the components (salt/solvent/inorganic material) thesolvent is removed via distillation. The resulting catalyst compositioncan be used to effectively cure epoxy resins.

Operable solvents include water and the oxy-containing solvents such asthe alcohols, glycols and glycol ethers as well as the ketones and otherorganic solvents. Suitable solvents include tetrahydrofuran (THF),acetone, methyl ethyl ketone (MEK), methyl isobutyl ketone (MIBK),pyran, propylene carbonate, cyclohexanone, acetophenone, diethyl ether,ethylene glycol, OXITOL®, CELLOSOLVE® and CELLOSOLVE® Acetate,morpholine, ethyl alcohol, dimethylsulfoxide (DMSO), dimethylformamide(DMF) and the like.

Suitable inorganic materials include silica gel, alumina, CABOSIL®,mica, clays, talcs, glasses, asbestos, gypsum, anhydrous CaSO₄, titaniumdioxide (TiO₂) and the like.

The following examples are given to illustrate the present heat-curablethermosetting compositions. It is understood that the examples areembodiments only and are given for the purpose of illustration and theinvention is not to be regarded as limited to any specific componentsand/or specific conditions recited therein. Unless otherwise indicated,parts and percentages in the examples, are parts and percentages

Epoxy Resin A is a liquid glycidyl polyether of2,2-bis-(4-hydroxyphenyl)propane having an epoxide equivalent (WPE) of175-190 and an average molecular weight of about 350.

Epoxy Resin B is a solid glycidyl polyether of2,2-bis(4-hydroxyphenyl)propane having a WPE of about 500 and an averagemolecular weight of about 900.

EXAMPLE I

Into a 500 ml beaker were placed 150 grams of Polyether A, a solution of1.5 g OXITOL® and 0.75 of LiBF₄. The mixture was stirred untilhomogenous and poured into a "HDT" mold to produce test specimens of1/2"×1/2"×5" and a "plate" mold 4"×8"×1/8". The material was set asideat ambient temperature for 1 hour (exotherm observed) and then cured at70° C. for 7 hours and post cured at 120° C. for 2 hours. The curedcomposition had the following physical properties:

    ______________________________________                                        HDT                     75° C.                                         Extension @ Break       2.3%                                                  tensile stress at                                                             break, psi              7000                                                  Young's modulus, psi    510,000                                               Izod, ft-lbs/in notch   0.3                                                   Retention of shear                                                            modulus at 70° C.;                                                     percentage of ambient                                                         temperature shear                                                             modulus retained at                                                           70° C. in a torsion                                                    test                    51%                                                   ______________________________________                                    

EXAMPLE II

Into a 25 ml polypropylene beaker were placed 10 grams of Polyether Aand a solution containing 0.1 grams LiBF₄ and 0.1 gram of water. Themixture was stirred rapidly and 2 grams of this mixture were placed in avial immersed in an oil bath at 150° C. The mixture exothermed to 236°C. in 66 seconds and upon being removed from the bath was a solid curedmass.

EXAMPLE III

The procedure of Example II was essentially repeated wherein NaBF₄,KBF₄, NH₄ BF₄ and NH₄ PF₆ were each used in lieu of LiBF₄ and OXITOL®was substituted for water. After heating at 100° C. to 150° C. forperiods exceeding 1 day, no appreciable gel was observed, thusindicating clearly the general ineffectiveness of the Na, K and NH₄salts of fluoboric acid.

EXAMPLE IV

10 grams of Polyether A were mixed with a solution containing 0.1 gram(Ca(BF₄)₂ and 0.2 g OXITOL®. After rapid mixing by hand, the mass curedand solidified within 20 seconds after the initial contact at roomtemperature.

EXAMPLE V

The procedure of Example IV was essentially repeated using the followingcompositions:

    ______________________________________                                                     Parts by Weight                                                  ______________________________________                                        Composition A                                                                 Polyether A    10                                                             Mg(BF.sub.4).sub.2                                                                           0.10                                                           Water          0.23                                                           Composition B                                                                 Polyether A    10                                                             Ca(BF.sub.4).sub.2                                                                           0.10                                                           OXITOL®    0.25                                                           ______________________________________                                    

The compositions were stirred by hand, poured on a gel plate and spreadwith a doctor blade into an 10 mil film. The film from Composition Acured hard in less than 30 minutes at room temperature and could bepeeled from the plate. The film from Composition B cured in 1 hour and15 minutes at room temperature. No significant exotherm was observed inthese thin films, indicating truly ambient cure.

EXAMPLE VI

The procedure of Example IV was repeated wherein no solvent wasemployed. Similar results were obtained.

EXAMPLE VII

The procedure of Example IV was repeated wherein an equivalent amount ofthe following solvents were used: tetrahydrofuran, acetone, MIBK, MEK,acetophenone, cyclohexanone, diethyl ether, ethylene glycol andpropylene carbonate. Similar results were obtained.

EXAMPLE VIII

The procedure of Example I was essentially repeated wherein 10 grams ofEpoxy Resin B were ground, mixed with 0.1 gram of LiBF₄ (dried invacuum) and placed on a 100° C. gel plate. The solid resin melted andgelled in 42 seconds and full hardness was exhibited 2 hours. The curedresin could not be melted again, thus proving it had cured. Neat EpoxyResin B can be melted and remelted.

EXAMPLE IX

This exaple illustrates the preparation of a preferred metal catalyst(curing agent) powder. 1 gram of LiBF₄ was dissolved in 10 grams ofOXITOL®. Then, 1 gram of CABOSIL® was added and stripped under vacuumfor 4 hours at 40° C. 3.18 grams of white free-flowing powder wereobtained.

One hundred parts by weight of Polyether A and of Polyether B could beeffectively cured with 3 parts by weight of the above curing agent inless than 20 minutes at room temperature.

EXAMPLE X

The procedure of Example IX was essentially repeated wherein a catalystwas prepared by mixing 0.27 grams of Ca(BF₄)₂.4H₂ O, 0.42 grams ofOXITOL® and 0.31 grams of CABOSIL® (fumed silica). Then 0.1 grams of theresulting dry catalyst was mixed with 0.85 grams of Epoxy Resin A in ahole 1/2" deep and 1/4" in diameter in the side of a 42 pound Portlandconcrete block by agitating a 3/16" eye bolt for thirty seconds. After 3minutes, it was possible to lift the concrete block by the eye bolt.

EXAMPLE XI

The procedure of Example X was essentially repeated wherein mica, silicagel, talc, anhydrous CaSO₄, and Bentonite clay was used in lieu ofCABOSIL®. Essentially the same results were obtained except that morecatalyst based on Bentonite clay was required to produce a good cure,i.e. ca 5 phr or more.

EXAMPLE XII

The example illustrates the effectiveness of the instant metal salts ascuring agents for epoxy resins. The components were mixed together andthe gel (cure) time was determined at preselected temperatures. Theresults of representative experiments are tabulated in Table I.

                  TABLE I                                                         ______________________________________                                        Pol-                                                                          y-          Curing         Solvent/                                           ether                                                                              pbw    Agent     pbw  pbw     Gel Time &/Temp.                           ______________________________________                                        A    100    Ca(BF.sub.4).sub.2                                                                      1    OXITOL  20 sec./RT (1 hr                                                      2       10 min in a                                                                   film RT)                                   A     80    Ca(BF.sub.4).sub.2                                                                      1    OXITOL  18 sec/100° C.                                                 20                                                 A    100    LiPF.sub.6                                                                              1    OXITOL  <21/2 min/RT                                                          2                                                  A    100    LiBF.sub.4                                                                              1    H.sub.2 O 1                                                                           66 sec/150° C.                      A    100    Mg(BF.sub.4).sub.2                                                                      1    H.sub.2 O 2.3                                                                         <30 min, RT-10 mil                                                            film                                       A    100    Ca(BF.sub.4).sub.2                                                                      1    Toluene 21/2 min, RT                                                          100 cyclo-                                                                    hexanone 2                                         A    100    Mg(BF.sub.4).sub.2                                                                      1.2  Toluene 1.3 min, RT                                                           100 cyclo-                                                                    hexanone                                                                      2.2                                                B    100    LiBF.sub.4                                                                              1    --      0.7 min, 100° C.                    ______________________________________                                          What is claimed is:

1. A curable composition consisting essentially of ( 1) at least oneepoxy compound containing at least one vicinal epoxy group and (2) acuring amount of a lithium salt of a nonnucleophilic acid.
 2. Thecomposition of claim 1 wherein the epoxy compound is a glycidylpolyether of a polyhydric phenol.
 3. The composition of claim 2 whereinthe polyhydric phenol is 2,2-bis(4-hydroxyphenyl)propane.
 4. Thecomposition of claim 1 wherein the lithium salt is LiBF₄ or LiPF₆.